This is all great information and debate. One thing that no one has touched on is the fact that the boat currently has no holding tank. So I was wondering about installing that vs. a composting head. We are going to have to do something. Now that I've read about pros and cons of each, which is more expensive in the short and long term?

Full installation of a new marine head (toilet, plumbing, thru-hulls, holding tank, labour) will very likely set you back as much or more than a new composting head. If it were just the toilet, then you can do it cheaper, although good quality heads (not those cheapo Jabscos) are still in the $500 range. A Nature's Head or Air Head will cost around $1,100. CHeads are even cheaper.

In the long term it's really a no-brainer. You'll never pay for another pump out with a composting head. Unless you're dumping out at sea, a standard head will certainly cost more over time.